A primary estimation of surface water distribution in China
Chensheng Shi, Ryotaro Tateishi
Remote Sensing and Image Research Center
Chiba University,
1-33 Yayoi-Cho, Inage-Ku, Chiba-city, Chiba 263 Japan
Koji Kajiwaa
Institute of Industrial Science,
University of Tokyo,
7-22 Roppingi Minato-Ku, Tokyo 106 Japan
Abstract
There is an urgent need to know available water resources in every part of China in order to establish efficient usage of water resources. For this reason, we tried to develop a method for estimating the distribution of water resources using Digital Elevation Model (DEM) data and rainfall data. The inflow and outflow on every cell of mesh data have been calculated one by one, using the method of tracing rainfall water flowing on the land surface. The study mainly uses the DEM data, rainfall data, the data files of rivers network and lakes position and the amount of flowing water of the largest seven rivers in China. We have considered all the main factors which affect the distribution of water resources, while paid more attentions on the factors of rainfall and topographic expressions in our present study. The amount of flowing water of the largest seven rivers in China were used to determine the evaporative proportions of corresponding river basin. As a result of this study, a water resources distribution map of the mainland of China has been produced.
1. Introduction
In China, there is a large problem of unbalanced distribution of water resources. Besides of the seasonal unbalance of water resources distribution, there is a more malignant areal unbalance of water distribution. For the purpose of using water4 resources more efficiently, we tried to analyze the distribution of water resources primarily by using topographic data. The processing used in the study include the tracing rainfall water flowing on the land surface mainly and some other methods.
2. Study area and data
2.1 Study area
The study area spreads from 700 E to 140E0 of longitude, and from 200 N to 550 N of latidude. The files we used are 5 minute’s mesh data files and, thus, they have about 9.31 km’s grid ( exactly, the grid is about 5.345 km at 550 N latitude and about 8.435 km’s wide at 250 N latitude on the latitudinal direction. While the gird is about 9.31 km’s long at any degrees of latitude on longitudinal direction). The study area is wide extent which has 700 of longitude and 350 of latitude. And so these mesh data files have the scale of 840 pixels in one record for 420 records.
2.2. Data files
As shown in Figure I, we have used topographic data ( DEM data) , annual rainfall data, river network and lake position data in the study, and we have also used a map of Chinese river basins, for helping to make the river basin masking.
Currently, we have used DEM data chiefly, for tracing of the rainfall water flowing on land surface based on DEM data. We stressed the importance of land cover data and soil specifications for the processing of tracing flow of water on the land surface. We sill use them in further studies of this field.
Figure 1: Schematic Diagram of Processing
3. Methodology
In order to use the method of tracing rainfall water flowing on land surface for estimating the distribution of water resources, three data processing steps have been carried out.
3.1 Preparation of data files
In our study, the most important data file is topographic data, because the rainfall water will flow due to the topographic condition the directions of flowing pathway and branching flow of water are decided mainly by the elevation, exactly by the slopes of central pixel to all eight neighbors. We got topographic data from ETOPO5 data file which is a global elevation data file. This file expresses all elevation by 4260 ( pixel ) x 2160 (line ) digital values, We can consider it as a 5 minute’s mesh picture of DEM ( Digital Elevation Model ) and the data of the study area have been separated from the ETOPO5 data file.
The another important data file is rainfall data. We got it from “Grid Data of World Temperature and Precipitation” which includes annual and monthly temperature and rainfall data of all over the world. But there was a problem of resolution. Because the data files have size of 1024 ( pixel) x 480 ( line) over the world, and it is 21 minute’s mesh data. So we have to interpolate it into 5 minute’s mesh file, in order to put all files together.
In our study, we also need to know the locations of rivers and lakes. We get them from “World Data Bank 2” provided by CIA. We have selected the rivers in study areas and change it’s position into 5 minute’s mesh files coordinate and finally wrote them respectively into two data files. They are network of rivers and position of lakes respectively.
